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Brachial plexus
This document discusses the electrophysiological evaluation of the brachial plexus using nerve conduction studies and electromyography. It describes the anatomy of the brachial plexus including its roots, trunks, divisions, cords, and terminal nerves. It explains how to assess each element of the brachial plexus using sensory nerve action potentials, compound muscle action potentials, and electromyography findings. It also discusses the patterns seen with different types of brachial plexus lesions and provides guidance on timing of electrodiagnostic testing and prognostication.
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Brachial plexus
- 1. Electrophysiology topic EDX evaluationof brachial plexus-An approach
- 2. Brachial plexus • Oneof the most complex and largest PNS structure • Highly vulnerable • Extensive non routine NCS • Time consuming • Contra lateral asymptomatic limb also needs to be studied
- 4. Anatomy • 100,000-160,000 nervefibers • Intermingle to form various brachial plexus elements • Roots • Trunks • Divisions • Cords • Terminal nerves
- 6. Roots • Dorsal andventral rootlets, dorsal and ventral roots, mixed spinal nerve in inter vertebral foramina, posterior primary rami and anterior primary rami • Surgeons VS anatomists • C5,C6,C7,C8,T1 • Prefixed, Post fixed • Cannot be studied by per cutaneous stimulation • Nerves arising from roots-dorsal scapular, long thoracic,phrenic
- 8. Trunks • Named aftertheir relationship to one another • C5-C6 APR-upper trunk • C7-middle trunk • C8-T1-lower trunk • Nerves from proximal upper trunk- suprascapular, nerve to subclavius • Mid and distal trunks can be stimulated in supraclavicular fossa and axilla
- 10. Divisions and cords •Each trunk divides into two. lie behind clavicle • Lateral cord-anterior divisions of upper and middle trunk C5-7roots • Medial cord-continuation of anterior division of lower trunk C8-T1roots • Posterior cord-posterior division of all trunks C5- C8 roots • Cord elements can be stimulated percutaneously
- 12. Nerves from cords •Lateral cord-lateral pectoral, musculo cutaneous, lateral head of median, lateral ante brachial cutaneous. • Posterior cord-sub scapular, thoraco dorsal, axillary, radial • Medial cord-medial pectoral, medial ante brachial cutaneous, medial brachial cutaneous, medial head of median nerve, ulnar • Terminal nerve elements can be studied by percutaneous stimulation
- 14. Classification of brachialplexus lesion • Supra clavicular VS infra clavicular • Supra clavicular-commoner, severe and worse prognosis Upper plexus-better, conduction block, proximity to muscles, extra foraminal and repairable Lower plexus-worse, axon loss, foraminal lesions, distal far muscles
- 15. EDX manifestations of pathophysiology •Axon loss • Demyelinative-conduction block or conduction slowing Good prognosis. stimulation site dependent distal to lesion –normal NCS proximal stimulation-axilla and erb’s point weak muscle, N cmap-EMG shows MUP dropout
- 16. Axon loss lesions •Most common • Wallerian degeneration 2-3 days later • Decreased SNAP,CMAP amplitude, norm al distal latencies and conduction velocities • Needle EMG-fibrillation potentials, MUP drop out (High innervation ratio in limbs)
- 17. Severity of lesion •CMAP amplitudes correlate well with amount of axonal loss in one to one ratio • Minimal lesion-EMG fibrillations Normal SNAP,CMAP • More severe-SNAP amps decrease • Greater severity-absent SNAP,CMAP amp decreased, MUP dropout
- 18. Timing of EDX •MUP dropout-immediately but severe • CMAP amps-begin to decrease on day 2- 3,reach nadir by day -7 • SNAP amp-begins to drop on day 6 and reach nadir on day 10-11 • Fibrillation potentials-may take10- 21 days to appear
- 19. Prognostication • Re innervationis by collateral sprouting and proximo distal regeneration • Depends on grade and completeness of injuries, distance between site of injury and innervated muscle • Regeneration is at 1 inch/month, denervated muscle fibers survive for 18-24 months. so distance more than 2 feet bad prognosis • Reinnervation normalises CMAP amps but alters morphology and recruitment
- 20. prognosis • No timelimit for sensory nerve regeneration • End organs of sensory nerve fibers donot undergo degeneration • Reinnervation successful even after two years • SNAP amplitude decrement correlates well with sensory loss
- 21. SNAPs -importance • Sensoryfibers are more sensitive to axon loss than motor fibers. Isolated SNAPs abnormalities do not rule our motor axon involvement • Intra spinal lesions do not affect sensory conduction. but affect motor NCS and EMG • Pattern of sensory loss localises lesion to brachial plexus elements much before motor NCS. • Motor anormalities with normal SNAPs are seen in-myopathies, preganglionic lesions, NMJ, early GBS, study before 6 days
- 22. EDX assessment ofbrachial plexus • Each brachial plexus element has- Muscle domain/EMG domain SNAP domain CMAP domain Domains of a distal element is sum of domains of all elements forming it minus domains of elements departing prior to formation of the element
- 23. Root domains • C5APR- no SNAP domain CMAP domain-Musc-biceps, Ax-deltoid EMG domain-C5 myotome • C6 APR-SNAP domain-LABC(100%),Med- D1(100%),s-radial(60%),Med-D2(20%),Med- D3(10%) CMAP domain-Musc-biceps, Ax-deltoid EMG domain-C6 myotome
- 24. Root domains • C7APR:SNAP- Med-D2(80%),Med-D3(70%),S- radial(40%) No dependable CMAP domain EMG-C7 myotome • C8 APR:SNAP domain uln-D5 CMAP domain: uln-ADM, uln-FDI, Rad- EIP, Med-APB EMG –C8 myotome • T1 APR:SNAP-MABC CMAP-Med-APB plus C8 cmap
- 28. EMG domains • Uppertrunk-(C5 plus C6) minus dorsal scapular, long thoracic nerve. • Middle trunk-C7 domain minus serratus anterior • Lower trunk-C8 plus T1 APR • Lateral cord-upper and middle trunks minus supra scapular, subscapular, thoraco dorsal, radial, axillary nerve • Posterior cord-sum of sub scapular, thoraco dorsal ,axillary and radial • Medial cord-lower trunk minus posterior division elements
- 29. Nerve domains • Axillarynerve-no SNAP domain CMAP domain: AX-deltoid EMG :innervated muscles • Musculo cutaneous: SNAP-LABC CMAP domain: AX-deltoid EMG- • Radial :SNAP-s radial CMAP: Rad-EDC,nRad-EIP EMG-radial and posterior interossei
- 30. Nerve domains • Median:SNAP domain- Med-D1,Med- D2,Med-D3 CMAP domain-Med-APB • Ulnar nerve: SNAP domain-Uln-D5 CMAP domain-uln-ADM, uln-FDI.
- 33.